1. Technical Field
The present invention relates to a method of adjusting an output signal level and a liquid ejecting apparatus operable to execute the same.
2. Related Art
As an ink jet printer that performs printing on a printing medium such as paper, there is known an ink jet printer comprising: a printing head that ejects ink droplets onto a printing medium; and a carriage mounting the printing head. In this kind of ink jet printer, an optical sensor having a light emitting element and a light receiving element is widely used. For example, in an ink jet printer, an optical sensor is used as a detector for detecting an edge of a printing medium loaded inside the ink jet printer. The optical sensor is fixed on a bottom face side of a carriage. Such a configuration is disclosed in Japanese Patent Publication No. 2005-81750A (JP-A-2005-81750).
On the other hand, Japanese Patent Publication No. 2001-113709A (JP-A-2001-113709) discloses an ink jet printer that uses an optical sensor as a detector for testing whether or not ink droplets are ejected from a printing head. The optical sensor is fixed to a body frame of the printer at the position corresponding to the home position of a carriage. Moreover, in order to perform an appropriate test a level adjustment of a signal output from the detector is made by adjusting an output gain of a light receiving element included in the detector.
In the ink jet printer, it is known that an ink mist (a part of ink droplets floating in the air in the form of mist) is generated and the generated ink mist adheres to each component inside the printer when ink droplets are ejected from a printing head before the ink droplets arrive at the surface of a printing medium. For example, the ink mist adheres to a light emitting face of a light emitting element or a light receiving face of a light receiving element included in a detector. Furthermore, it is known that a light emission amount of a light emitting element generally decreases as time goes by.
Thus, in the optical sensor used in the ink jet printer, an output signal level changes due to the influence of the ink mist, temporal decrease of the light emission amount, and the like. As a result, the detection accuracy of the optical sensor used in the ink jet printer deteriorates. Particularly in the case of a commercial ink jet printer that performs printing on a large-sized printing sheet, such as an A1 or A2 (defined by Japanese Industrial Standard) sheet, an amount of ejected ink is large and a period of time for which the detector is used is long (that is, light emission time of a light emitting element is long). Accordingly, there occurs a problem that the detection accuracy of the detector deteriorates.
In addition, in recent years, an ink jet printer capable of performing highly precise printing is demanded in the market. Particularly in the commercial printer, improvement in the printing accuracy is required. For this reason, particularly in the case when an optical sensor is used as a detector for executing a printing control, the printing accuracy deteriorates in accordance with the deterioration of the detection accuracy of the detector.